Super-high-molecular-weight polyolefin yarn, method for producing same, and drawing device

ABSTRACT

An ultrahigh molecular weight polyolefin yarn of the present invention has been drawn and has a melting point that is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min, and the melting point is higher than a melting point of the yarn before drawing. In a production method of the present invention, a drawing bath ( 3 ) that includes a hollow yarn path ( 14 ) and a jacket portion ( 13 ) in which a heated liquid circulates is placed in a drawing zone, and the yarn is heated and drawn while passing through the yarn path ( 14 ) in a non-contact manner. A drawing device of the present invention includes a feeder ( 1 ) for feeding a yarn, a drawing bath ( 3 ) for heating and drawing the yarn, and a winder ( 5 ) for winding up the drawn yarn. The drawing bath ( 3 ) includes a hollow yarn path ( 14 ) and a jacket portion ( 13 ) in which a heated liquid circulates. Thus, the present invention provides a drawing method in which a high strength ultrahigh molecular weight polyolefin yarn can be drawn stably even at a high draw ratio, a drawing device, and a yarn obtained by the drawing method.

TECHNICAL FIELD

The present invention relates to a high strength ultrahigh molecularweight polyolefin yarn, a method for producing the same, and a drawingdevice.

BACKGROUND ART

High strength polyolefin filaments, typified by gel spun ultrahighmolecular weight polyethylene filaments, have high tenacity, lightweight, and excellent light and abrasion resistance, and therefore areused for ropes, fishing lines, reinforcing materials, protectiveclothing, or the like.

It is known that raw yarns, twisted yarns, or braided yarns of highstrength ultrahigh molecular weight polyolefin that have been drawn canbe postdrawn (redrawn). Postdrawing is also called redrawing. In thepresent specification, postdrawing or redrawing simply may be referredto as “drawing”. The melting point of the high strength ultrahighmolecular weight polyolefin is 120 to 240° C., although it depends onthe type of the resin. As a typical example, ultrahigh molecular weightpolyethylene has a melting point of 138 to 162° C. The followingdocuments are directed to polyethylene. Patent Document 1 discloses thatdrawing is performed at a temperature not higher than the melting point(140 to 153° C.). Patent Document 2 discloses that a braided fishingline is fused and drawn to 1.01 to 2.2 times at a temperature within themelting point range (150 to 155° C.). Patent Document 2 also disclosesthat the fishing line thus drawn under the above conditions increasesthe transparency due to the fusion and becomes like a monofilament.

Patent Documents 3, 4, 5, etc. disclose drawing at a high draw ratio. InPatent Document 3, a forced convection oven is used as a drawing device,and a yarn is drawn to 3 times or more at 130 to 160° C. In PatentDocument 4, a yarn is drawn to 2.7 times or more at 150 to 157° C. InPatent Document 5, a polyolefin yarn is drawn to 2 times or more to havea single fiber fineness of 0.55 deci tex or less. Patent Documents 3 and4 use filaments having a large single fiber fineness and a large totalfineness. Patent Document 5 teaches that it is desirable that yarns aredoubled to increase the total fineness and then drawn, thereby achievinga small single fiber fineness.

According to the studies conducted by the present inventors, thetemperature of a drawing bath needs to be controlled with high precisionso that drawing can be performed at a high draw ratio within a narrowmelting point range, as described above, to establish industriallystable production. As an example of a drawing device for high strengthpolyolefin, Patent Document 3 uses a forced convection oven. AlthoughPatent Document 4 does not specifically teach a drawing device, Patent

Document 6 (by the same applicant as Patent Document 4) discloses anair-blow drawing device that provides a gas flow in the directionperpendicular to the yarn.

The drawing system that blows and circulates a heated gas such as airgenerally has been used for the drawing of a monofilament When thisdrawing system requires high-precision temperature control, it isdesirable that the gas flow rate is increased so as to increase thenumber of circulations of the gas per unit time. However, a strong gasflow can cause the yarn to sway and tangle, and thus makes the drawingunstable. On the other hand, if the gas flow rate is reduced, the numberof circulations of the gas per unit time is reduced. This is likely toresult in an uneven temperature distribution in the drawing bath (e.g.,between the inlet and the outlet, the center and the ends, or the like)and temperature variations over time. In particular, when the totalfineness and the single fiber fineness of the yarn are small, the yarnand the single fiber are broken easily even by a relatively smallfluctuation, and it is more difficult to perform the drawing stably.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JPS 61(1986)-289111 A

Patent Document 2: JPH 9(1997)-98698 A

Patent Document 3: JP 2008-512573 A

Patent Document 4: JP 2008-517168 A

Patent Document 5: 2008-266843 A

Patent Document 6: 2004-512436 A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

To solve the above conventional problems, the present invention providesa method for producing a high strength ultrahigh molecular weightpolyolefin yarn, in which the yarn can be drawn stably even at a highdraw ratio, a drawing device, and a yarn produced by this method.

Means for Solving Problem

An ultrahigh molecular weight polyolefin yarn of the present inventionhas been drawn and has a melting point that is determined as a maximumpeak temperature measured by a differential scanning calorimeter (DSC)at a temperature rise rate of 20° C./min. The melting point is higherthan a melting point of the yarn before drawing.

A method for producing an ultrahigh molecular weight polyolefin yarn ofthe present invention includes heating and drawing the ultrahighmolecular weight polyolefin yarn. A drawing bath that includes a hollowyarn path and a jacket portion in which a heated liquid circulates isplaced in a drawing zone. The yarn is heated and drawn while passingthrough the yarn path in a non-contact manner.

A drawing device of the present invention is used in the above methodfor producing an ultrahigh molecular weight polyolefin yarn, andincludes a feeder for feeding a yarn, a drawing bath for heating anddrawing the yarn, and a winder for winding up the drawn yarn. Thedrawing bath includes a hollow yarn path and a jacket portion in which aheated liquid circulates.

Effects of the Invention

The melting point of the drawn ultrahigh molecular weight polyolefinyarn of the present invention, which is determined as a maximum peaktemperature measured by a differential scanning calorimeter (DSC) at atemperature rise rate of 20° C./min, shifts to a higher temperature thanthe melting point of the yarn before drawing. This indicates thatcrystallization or melt-recrystallization of the amorphous portionproceeds by uniform drawing, and a skin-core structure composed of thesurface layer and the inside of a filament is reduced or eliminated, sothat the filament is changed into a crystal structure that is uniform inthe cross-sectional direction. According to the present invention, thehigh strength ultrahigh molecular weight polyolefin yarn can be drawnstably even at a high draw ratio, and an extra-fine drawn yarn having asmall total fineness can be provided. Moreover, the present inventioncan provide an ultrahigh molecular weight polyolefin yarn that has asmall coefficient of variation in strength and excellent uniformity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic process diagram showing the whole of a drawingdevice of an example of the present invention.

FIG. 2 is a perspective view of a drawing bath of an example of thepresent invention.

FIGS. 3A to 3C are cross-sectional views of a drawing bath of an exampleof the present invention.

FIG. 4A is a DSC chart of a yarn before drawing in Examples 1 and 4.FIG. 4B is a DSC chart of a yarn after drawing in Example 1.

FIG. 5 is a DSC chart of a yarn at a draw ratio of 2.0 times in Example4.

FIG. 6 is a DSC chart of a yarn at a draw ratio of 2.5 times in Example4.

FIG. 7 is a DSC chart of a yarn at a draw ratio of 3.0 times in Example4.

FIG. 8 is a DSC chart of a yarn at a draw ratio of 5.6 times in Example4.

FIG. 9 is a DSC chart of a yarn at a draw ratio of 1.5 times inComparative Example 4.

FIG. 10 is a DSC chart of a yarn at a draw ratio of 2 0 times inComparative Example 4.

DESCRIPTION OF THE INVENTION

The present inventors have found that when an ultrahigh molecular weightpolyolefin yarn is drawn uniformly by the drawing method of the presentinvention, the melting point of the resulting drawn yarn, which isdetermined as a maximum peak temperature measured by a differentialscanning calorimeter (DSC) at a temperature rise rate of 20° C./min inthe unconstrained state, shifts to higher temperatures due to thedrawing, and the maximum peak temperature (melting point) is even higherthan the melting point of the yarn before drawing.

With respect to the ultrahigh molecular weight polyethylene yarn, acommercially available high tenacity polyethylene yarn, i.e., aconventional drawn yarn has a melting point of about 147 to 153° C. Thepresent invention demonstrates that the drawn yarn obtained by redrawingthe conventional drawn yarn has a maximum peak temperature of 155 to162° C. (i.e., a high temperature peak). This high temperature peak mayexist independently or in conjunction with a shoulder or small peak thatis in the vicinity of the melting point (147 to 153° C.) before drawing.In either case, if the draw ratio is high, the maximum peak temperaturereaches a high temperature of 155 to 162° C. The melting point afterdrawing is higher than the drawing temperature, indicating that thedrawing has changed a large proportion of the structure and made thestructure highly uniform. Such a component having a high melting pointalso can be recognized as a small peak or shoulder in the DSC of the rawyarn before drawing. However, in the conventional raw yarn and drawingmethod, it is not known that the component having a high melting pointshows the main peak. Therefore, the above phenomenon may indicate thatcrystallization and melt-recrystallization of the amorphous portionproceeds by uniform drawing, and a skin-core structure composed of thesurface layer and the inside of a filament is reduced or eliminated, sothat the filament is changed into a crystal structure that is uniform inthe cross-sectional direction.

The degree of crystallinity calculated from the amount of heat of fusionis 72 to 85% after drawing, which is likely to be the same as orslightly larger than the degree of crystallinity (65 to 80%) beforedrawing. These features can support the fact that the drawing of thepresent invention is performed uniformly under high-precisiontemperature control.

On the other hand, in the conventional hot air circulation drawing, themain peak appears at a temperature of 147 to 153° C. on the lowtemperature side even after drawing, and the structural change due tothe drawing is smaller than that in the drawing method of the presentinvention. The degree of crystallinity calculated from the amount ofheat of fusion is 70 to 85% after drawing.

The ultrahigh molecular weight polyolefin of the present inventionincludes polyethylene, polypropylene, polybutene-1,poly(4-methylpentene-1), and copolymers or mixtures thereof Theultrahigh molecular weight is preferably an average molecular weight ofat least about 200,000, and more preferably at least about 600,000.Here, the molecular weight represents a weight average molecular weight(Mw) and can be calculated by Mw =5.37×10⁴×[IV]^(1.37), where [IV] is anintrinsic viscosity in decalin at 135° C. (Patent Document 4 etc.).

The polyolefin yarn of the present invention is preferably a highstrength filament that is produced by a so-called “gel spinning” methodand has a strength of at least 15 CN/dtex.

In particular, a high strength ultrahigh molecular weight polyethylenefilament is suitable. Examples of the high strength polyethylenefilament include “Dyneema” (trade name) manufactured by TOYOBO CO., LTD.and DSM Corporation, and “Spectra” (trade name) manufactured byHoneywell Inc.

In the context of the present invention, the yarn is preferably anuntwisted, interlaced, twisted, or braided multifilament yarn.

Next, examples of a drawing method and a manufacturing apparatus of thepresent invention will be described with reference to the schematicdrawings. The same components or materials are denoted by the samereference numerals. FIG. 1 is a schematic process diagram showing thewhole of a drawing device in an example of the present invention. FIG. 1is an overall view of a one-stage drawing device. A plurality of feedyarns 8 (8 yarns in FIG. 1) are pulled out of a yarn feeder 1, fed to afirst roller group 2 rotating at a speed V1, heated and drawn in adrawing bath 3, drawn on a second roller group 4 at a speed V2, and thenthe drawn yarns 9 are wound up by a winder 5. The total draw ratio isexpressed by V2/V1. A yarn path 14 of the drawing bath 3 is hollow, andthe yarns are heated and drawn in the yarn path 14. A heated liquidcirculates in a jacket portion 13 enclosed by a housing portion 16 ofthe drawing bath 3. The circulating liquid is heated at a predeterminedtemperature by a heater 6, and is forced to circulate using a pump 7that is located upstream or downstream of the heater 6. Although thisexample shows one-stage drawing, multi-stage drawing (with two or morestages) may be used. The number of drawing baths and the length of thedrawing bath are not particularly limited, and can be appropriatelyselected.

FIG. 2 is a perspective view of the drawing bath 3 in an example of thepresent invention. The yarn path 14 is in the form of a continuouscavity. The feed yarns 10 a to 10 c are heated and drawn so as not to bein contact with the drawing bath 3, and the drawn yarns 11 a to 11 c arewound up. The drawing bath 3 may have any length L as long as it is longenough to be able to heat and draw the feed yarns 10 a to 10 cuniformly, although the length L depends on the speed of the yarn andthe draw ratio. The practically favorable length L of the drawing bath 3is 0.3 to 10 m, and more preferably 0.5 to 5 m. If the length L is toolong, temperature variations are likely to occur in the lengthdirection. Therefore, it is desirable that two or more units are coupledas needed.

FIGS. 3A to 3C are cross-sectional views (taken along the directionperpendicular to the traveling direction of the yarns) of the drawingbath 3 in an example of the present invention. In FIG. 3A, both thedrawing bath 3 and the yarn path 14 have an elliptical cross section.The yarns 10 a to 10 c are heated and drawn so as not to be in contactwith an inner wall 12 of the drawing bath 3. The heated liquidcirculates in the jacket portion 13. The yarn path 14 is in the form ofa continuous cavity. In FIG. 3B, both the drawing bath 3 and the yarnpath 14 have a rectangular cross section. However, each of the cornersis formed in an arc shape. In FIG. 3C, the drawing bath 3 has arectangular cross section, and the yarn path 14 has a circular crosssection. The minor axis 15, the height 15, and the diameter 15 of theyarn paths 14 in FIGS. 3A, 3B, and 3C are preferably in the range of 10to 300 mm, and more preferably in the range of 10 to 150 mm,respectively.

The heated liquid circulates through a temperature-controlled heatingmedium heater. The heated liquid is not directly in contact with theyarns, and therefore can circulate at a high speed. Moreover, if thecapacity of the jacket is made sufficiently large compared to the yarns,there is almost no temperature change due to the traveling of the yarns.The heated liquid is not particularly limited, and a general heatingmedium liquid such as oils preferably can be used. Although not shown,it is desirable that the outer wall of the drawing bath 3 is coveredwith a heat insulating material.

In the present invention, it is preferable that positive air ventilationis not provided in the drawing bath. In this case, the “positive airventilation” means forced air ventilation with the use of a fan or thelike. When the positive air ventilation is not provided, the internaltemperature hardly varies and the yarns do not sway, so that stabledrawing can be performed. Incidentally, natural convection is tolerated.

The drawing method of the present invention has the following advantagesover the hot air circulation drawing that is generally used as apostdrawing method of a polyolefin yarn.

(1) The present invention ensures excellent temperature control accuracy

(2) Since the present invention does not provide the positive airventilation, the yarn is stable even if it is a fine filament.

(3) The present invention mainly uses radiant heat from the inner walland natural convection, while the yarn is heated by the forcedcirculation of hot air in the hot air circulation system. Such adifference may also be one of the advantages of the present invention.

For the temperature control, the ambient temperature (drawingtemperature) of the drawing bath is preferably 150 to 157° C. and iscontrolled within ±0.2° C., and more preferably controlled within theambient temperature (drawing temperature) ±0.1° C. In this manner, thedrawing bath of the present invention enables stable temperaturecontrol. On the other hand, the conventional air-blow (hot aircirculation) drawing bath has a variation of about ±1.0° C. This isdescribed in Example 1 of Patent Document 3. The heating system of thepresent invention uses a liquid as a heating medium and forces theliquid to circulate, thereby improving the temperature accuracy.

It has been confirmed that there is less variation in temperatureaccording to the location in the drawing bath. In the air-blow drawingbath, the circulation velocity (blowing speed) may be limited due to theswaying of the yarn, and the temperature control accuracy may be limitedbecause the heat capacity of a gas is smaller than that of a liquid, anda nonuniform gas flow is likely to occur in the device.

The cross section of the yarn path 14 can be elliptical, rectangular,and circular, as shown in FIGS. 3A to 3C. However, the cross section ofthe yarn path 14 is not limited thereto, and may be appropriatelydesigned in accordance with the number of yarns to be drawn. Moreover,it is preferable that the entire surface of the inner wall of thedrawing bath, except for the inlet and the outlet through which theyarns pass, is jacket heated so as to make the temperature more uniform.

In this regard, if there is an opening or gap that is not jacket heatedin the inner wall of the drawing bath, such a structure is not suitable.Moreover, an opening and closing structure of the drawing bath is alsonot suitable, since the temperature is changed by opening and closingoperations, and it takes time before the temperature becomes constant.

The inlet and outlet of the drawing bath of the present invention areopen. However, if the opening space is large, the temperature varies asthe heated air comes in and out of the drawing bath. Therefore, it ispreferable that a temperature difference is reduced, e.g., by shieldingthe opening other than the portion where the yarn is traveling, or bydisposing a heat insulating material or a heating unit at a temperaturelower than the drawing bath temperature in front of the inlet and/orbehind the outlet of the drawing bath.

The length (L) of the drawing bath (unit) is not particularly limited,and a plurality of drawing baths may be coupled, or multi-stage drawingmay be performed as needed. In this case, the length (L) of the drawingbath means the total length of the drawing bath units.

The capacity of the heating medium and the size of the inside of thejacket are not particularly limited, and any structure may be used aslong as the internal temperature is uniform and does not vary even ifmany yarns are processed together.

However, if the cross section of the yarn path 14 is too large,temperature variations occur. On the other hand, if the cross section ofthe yarn path 14 is too small, the workability such as threading of theyarns through the yarn path is poor. Therefore, the preferred height,diameter, or minor axis of the cross section is about 10 to 300 mm. Itis desirable that the yarns 10 a to 10 c pass through near the centralportion of the yarn path 14 in terms of uniform heating.

In the present invention, the yarn to be drawn is a drawn ultrahighmolecular weight polyolefin multifilament yarn. The drawn feed yarn canbe an untwisted yarn, an interlaced yarn, a twisted yarn, or a braidedyarn. It is possible to use either a method in which the raw yarns suchas the untwisted yarns, the interlaced yarns, or the single-twistedyarns are drawn and then braided to form a product or a method in whichthe braided yarns are drawn to form a product, or both of these methods.The above methods may be selected as needed, and the raw yarns beforebraiding can be drawn at a higher draw ratio. If necessary, these yarnsmay contain oils such as mineral oil and vegetable oil, waxes, andresins such as polyolefin resin, modified polyolefin resin, andethylene-acrylic acid copolymer resin. Moreover, the resins may containa coloring agent.

The thickness (fineness) of the yarn to be drawn is not particularlylimited. Compared to the conventional air-blow heating, the drawingmethod of the present invention has the advantage of drawing a fineyarn. In view of this, it is particularly preferable that the finenessof the feed yarn is 400 dtex or less.

In the present invention, extra-fine yarns having a fineness of 50 dtexor less after drawing, which have been difficult to produceindustrially, can be produced and also applied to braided yarns. Suchextra-fine braided yarns can be obtained by a method in which the rawyarns before braiding are drawn by the drawing method of the presentinvention and then braided, a method in which the braided yarns aredrawn by the drawing method of the present invention, or a combinationof these methods. Although the single fiber fineness depends on that ofthe raw yarns before drawing, commercially available yarns with a singlefiber fineness of 1.1 dtex can be drawn into ultrafine yarns with asingle fiber fineness of 0.2 dtex or less. Such fine yarns and finebraided yarns are particularly suitable for fishing lines of a smallline size number. Moreover, since those yarns cannot be seen easily bythe naked eye and have high tenacity, they are suitable for strings forhanging, sutures, thin knitted fabrics, nets, or the like.

The ultrahigh molecular weight polyethylene yarn is drawn under theconditions that the temperature is preferably 150 to 157° C. and thedraw ratio is about 1.5 to 10 times. Setting the drawing conditions isimportant because if the temperature and the time are insufficient, theyarn is broken during the drawing, and if the temperature is too highand the time is too long, the yarn is broken by melting or becomes weakdue to excessive fusion. The residence time in the drawing bath ispreferably 0.1 to 8 minutes, although it depends on the temperature andthe draw ratio.

The drawing method of the present invention has the following advantagesover the conventional hot air circulation heating method.

(1) The present invention suppresses the breakage of the yarn during thedrawing and reduces fuzz on the yarn.

(2) The present invention allows the drawing to be performed at a highdraw ratio such that the maximum draw ratio is higher at the samedrawing temperature.

(3) There is only a small variation in the physical properties of thedrawn yarn.

(4) The present invention ensures high stability at the time of anincrease in quantity.

In addition to the general uniform drawing at a constant draw ratio, thepresent invention also can produce a tapered braided yarn with athickness ratio of about 1:5 to 1:8 by variably controlling the drawratio.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of Examples and Comparative Examples. However, the present inventionis not limited to the following examples.

Examples 1 to 3 used a drawing bath having a length of 3 m and a hollowrectangular cross section, as shown in FIG. 3B, in combination with aone-stage drawing device, as shown in FIGS. 1 and 2. ComparativeExamples used a hot air circulation drawing bath having the same lengthin place of the drawing bath in Examples 1 to 3.

Examples and Comparative Examples were evaluated in the followingmanner.

Physical Properties Test

The strength-elongation was measured according to the measurement methodof JIS L1013. The fineness (dtex) was determined by cutting a yarn intoa length of 1 m, measuring the weight of the cut yarn in units of 0.1mg, and multiplying the result by 10000.

Evaluation of Drawing Properties

The drawing properties were evaluated by the following criteria underthe respective drawing conditions.

A: No yarn breakage occurred for 5 minutes or more.

B: A yarn breakage occurred within 5 minutes, but the yarn was wound up.

C: A yarn breakage occurred immediately, and the yarn was not wound up.

Measurement of Melting Point and Degree of Crystallinity by DifferentialScanning Calorimeter (DSC)

Using a differential scanning calorimeter DSC-60 manufactured byShimadzu Corporation, the yarn was measured in the unconstrained stateat a temperature rise rate of 20° C./min. The maximum peak temperatureat a melting endothermic peak was defined as a melting point. The degreeof crystallinity was determined by the following formula based on theamount of endotherm Δ Hm (J/g) obtained from the peak area.

Degree of crystallinity (%)=100 ×Δ Hm/Δ H

where Δ H represents the amount of heat of fusion of a perfect crystal.In the case of polyethylene, the calculation was performed with Δ H=293J/g. When the sample yarns appeared to be in the constrained state as aresult of braiding, resin finish, or the like, the yarns weredisentangled before measurement.

The following yarns were used as raw yarns before drawing.

Raw Yarn Before Drawing

Raw yarn A: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”,110T-96F-410, single twisted (s-twist) with 90 twists per meter

Braided yarn B: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”,55T-48F-410, a set of four yarns

Braided yarn C: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”,165T-144F-410, a set of eight yarns

Example 1

A drawing test was performed using a single-twisted high strengthultrahigh molecular weight polyethylene raw yarn A, which had been drawnby the conventional method, as a feed yarn. In this example, the rawyarn A was obtained by twisting (s-twist) a raw yarn manufactured byTOYOBO CO., LTD., trade name: “Dyneema”, 110T-96F (total fineness: 110Tex; number of filaments: 96) with 90 twists per meter. The raw yarnused had a tensile strength of 31.8 CN/dtex, an elongation of 4.8%, aDSC melting point of 150.3° C., and a degree of crystallinity of 75%.FIG. 4A shows a DSC chart of the yarn before drawing. In FIG. 4A, adotted line is an auxiliary line that is automatically added by theanalyzer to determine a peak area. The same is true for the followingDSC charts. The drawing bath of the drawing device used had a length of3 m and a hollow rectangular cross section, as shown in FIG. 3B. Thedrawing test was performed with the one-stage drawing device, as shownin FIGS. 1 and 2. The measured temperature of the drawing bath was154±0.1° C., and the temperature was stable. The draw ratio was changedfrom 3.6 to 4.7 times, and consequently the maximum draw ratio was 4.6times, as shown in Table 1. The drawn yarn at this draw ratio had astrength of 35.7 CN/dtex, an elongation of 2.4%, a DSC melting point of157.5° C., and a degree of crystallinity of 80%. The melting point wasraised by about 8° C. and the degree of crystallinity was increased by5% due to the drawing. FIG. 4B shows a DSC chart of the drawn yarn at amaximum draw ratio of 4.6 times.

Comparative Example 1

A one-stage drawing test was performed on three yarns while increasingthe draw ratio using the same device as Example 1, except that a hot aircirculation drawing bath having a length of 3 m was used instead of thedrawing bath in Example 1. As shown in Table 1, the drawn yarn at a drawratio of 3.6 times could be wound up for 5 minutes or more. However, thedrawn yarn at a draw ratio of 3.7 times was broken in a little more than1 minute, and the drawn yarn at a draw ratio of 3.8 times was frequentlybroken and could not be wound up. Therefore, the maximum draw ratio was3.6 times in accordance with the criteria described above. The drawnyarn at this draw ratio had a strength of 30.6 CN/dtex and an elongationof 2.5%. The measured temperature of the drawing bath was 154±1.0° C.The drawn yarn at a draw ratio of 3 6 times had a DSC melting point of151.5° C. and a degree of crystallinity of 79%. Tables 1 and 2 show theconditions and the results of Example 1 and Comparative Example 1.

TABLE 1 Example/ Feed Winding Jacket heating Internal Fineness FinenessCompar- speed speed Draw medium temperature of before after ative Exper.V1 V2 ratio temperature drawing bath drawing drawing Example No. Sample(m/min) (m/min) (V2/V1) (° C.) (° C.) Results of drawing (dtex) (dtex)Ex. 1 1-1 Raw yarn A: 0.91 3.30 3.6 154.0 154 ± 0.1 A: No problem 109.530.5 110T 1-2 Raw yarn A: 0.72 3.30 4.6 154.0 154 ± 0.1 A: Maximum drawratio 109.5 23.8 110T Comp. 1-3 Raw yarn A: 0.91 3.30 3.6 154*  154 ±1.0 A: Maximum draw ratio 109.5 30.6 Ex. 1 110T 1-4 Raw yarnA: 0.89 3.303.7 154*  154 ± 1.0 B: The yarn was broken in 1 109.5 29.0 110T minuteand 15 seconds. 1-5 Raw yarn A: 0.87 3.30 3.8 154*  154 ± 1.0 C: Theyarn was frequently 109.5 — 110T broken. (Note) *Set temperature of ahot air circulation drawing bath

TABLE 2 Example/ DSC peak temperature DSC peak temperature Degree ofComparative Exper. Strength Elongation on low temperature on hightemperature crystallinity DSC chart Example No. (CN/dtex) (%) side (°C.) side (° C.) (%) No. Before drawing 1-0 31.8 4.8 ◯ 150.3 — 75 FIG. 4AEx. 1 1-2 35.7 2.4 — ◯ 158.6 80 FIG. 4B Comp. Ex. 1 1-3 34.9 2.5 ◯ 151.8  158.8 78 — 1-4 34.5 2.5 — — — — 1-5 — — — — — — (Note) ◯ Maximum peaktemperature (melting point)

As is evident from Table 1, Example 1 can significantly improve themaximum draw ratio compared to Comparative Example 1, and thus canstably provide the drawn yarn with a small fineness. The drawn yarn alsohas a high strength. Moreover, as is evident from Table 2, it can beconfirmed that the melting point measured as a maximum peak temperatureby the differential scanning calorimeter (DSC) at a temperature riserate of 20° C/min in the unconstrained state shifts 8.3° C. to the hightemperature side from the melting point of the yarn before drawing, andthe melting point thus measured is 7° C. higher than that of ComparativeExample 1. Further, the degree of crystallinity is higher in Example 1than in Comparative Example 1.

Example 2

A drawing test was performed using a braided yarn B as a feed yarn. Inthis example, the braided yarn B was obtained by braiding four raw yarnsmanufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 55T-48F (totalfineness: 55 Tex, number of filaments: 48). The braided yarn B used hada tensile strength of 25.4 CN/dtex and an elongation of 4.9%. Thedrawing test was performed with the same jacket heating drawing bath asExample 1. As shown in Tables 3 and 4, the maximum draw ratio was 3 2times in Example 2, which was improved compared to Comparative Example2. The drawn yarn at this draw ratio had a strength of 27.0 CN/dtex andan elongation of 2.9%.

Comparative Example 2

The maximum draw ratio was examined using a hot air circulation drawingbath in the same manner as Comparative Example 1. As shown in Table 2,the maximum draw ratio was 2.7 times. The drawn yarn at a draw ratio of2.9 times was frequently broken and could not be wound up. The drawnyarn at the maximum draw ratio had a strength of 26.5 CN/dtex and anelongation of 3.1%. Tables 3 and 4 show the conditions and the resultsof Example 2 and Comparative Example 2.

TABLE 3 Feed Winding Jacket heating Internal Fineness Fineness Example/speed speed Draw medium temperature of before after Comparative Exper.V1 V2 ratio temperature drawing bath drawing drawing Example No. Sample(m/min) (m/min) (V2/V1) (° C.) (° C.) Results of drawing (dtex) (dtex)Ex. 2 2-1 Braided yarn B 0.78 2.50 3.2 154.0 154 ± 0.1 A: Maximum drawratio 205.2 64.5 Comp. Ex. 2 2-2 Braided yarn B 0.93 2.50 2.7 154*  154± 1.0 A: Maximum draw ratio 205.2 76.3 2-3 Braided yarn B 0.89 2.50 2.8154*  154 ± 1.0 B: The yarn was broken 205.2 73.6 in 1 minute. 2-4Braided yarn B 0.86 2.50 2.9 154*  154 ± 1.0 C: The yarn was frequently205.2 — broken. (Note) *Set temperature of a hot air circulation drawingbath

TABLE 4 Example/ DSC peak temperature DSC peak temperature Degree ofComparative Exper. Strength Elongation on low temperature on hightemperature crystallinity Example No. (CN/dtex) (%) side (° C.) side (°C.) (%) Before drawing 2-0 25.4 4.9 ◯ 150.3  157.9 72 Ex. 2 2-1 27.0 2.9— ◯ 161.6 80 Comp. Ex. 2 2-2 26.5 3.1 ◯ 150.5   158.3 78 2-3 — — — — —2-4 — — — — — (Note) ◯ Maximum peak temperature (melting point)

As is evident from Table 3, Example 2 can significantly improve themaximum draw ratio compared to Comparative Example 2, and thus canstably provide the drawn yarn with a small fineness. Moreover, as isevident from Table 4, it can be confirmed that the melting pointmeasured as a maximum peak temperature by the differential scanningcalorimeter (DSC) at a temperature rise rate of 20° C./min in theunconstrained state shifts 11.3° C. to the high temperature side fromthe melting point of the yarn before drawing, and the melting point thusmeasured is 11.1° C. higher than that of Comparative Example 2. Further,the degree of crystallinity is higher in Example 2 than in ComparativeExample 2.

Example 3

A drawing test was performed using a relatively thick braided yarn C asa feed yarn. In this example, the braided yarn C was obtained bybraiding eight raw yarns manufactured by TOYOBO CO., LTD., trade name:“Dyneema”, 165T-144F (total fineness: 165 Tex, number of filaments:144). The braided yarn C used had a tensile strength of 23.7 CN/dtex andan elongation of 5.9%. The drawing test was performed with the samejacket heating drawing bath as Example 1. As shown in Table 3, themaximum draw ratio was 2.4 times in Example 3, which was improvedcompared to Comparative Example 3. The drawn yarn at this draw ratio hada strength of 26.0 CN/dtex and an elongation of 3.5%.

Comparative Example 3

The maximum draw ratio was examined using a hot air circulation drawingbath in the same manner as Comparative Example 1. As shown in Table 3,the maximum draw ratio was 2.1 times. The drawn yarn at the maximum drawratio had a strength of 25.5 CN/dtex and an elongation of 3.5%. Tables 5and 6 show the conditions and the results of Example 3 and ComparativeExample 3.

TABLE 5 Feed Winding Jacket heating Internal Fineness Fineness Example/speed speed Draw medium temperature of before after Comparative Exper.V1 V2 ratio temperature drawing bath drawing drawing Example No. Sample(m/min) (m/min) (V2/V1) (° C.) (° C.) Results of drawing (dtex) (dtex)Ex. 3 3-1 Braided yarn C 0.63 1.50 2.4 154.0 154 ± 0.1 A: Maximum drawratio 1260 603 Comp. Ex. 3 3-2 Braided yarn C 0.71 1.50 2.1 154*  154 ±1.0 A: Maximum draw ratio 1260 528 (Note) *Set temperature of a hot aircirculation drawing bath

TABLE 6 Example/ DSC peak temperature DSC peak temperature Degree ofComparative Exper. Strength Elongation on low temperature on hightemperature crystallinity Example No. (CN/dtex) (%) side (° C.) side (°C.) (%) Before drawing 3-0 23.7 5.9 ◯ 150.4   157.5 75 Ex. 3 3-1 26.03.5 — ◯ 157.2 85 Comp. Ex. 3 3-2 25.5 3.5 ◯ 150.5   157.5 82 (Note) ◯Maximum peak temperature (melting point)

As is evident from Table 5, Example 3 can significantly improve themaximum draw ratio compared to Comparative Example 3, and thus canstably provide the drawn yarn with a small fineness. Moreover, as isevident from Table 6, it can be confirmed that the melting pointmeasured as a maximum peak temperature by the differential scanningcalorimeter (DSC) at a temperature rise rate of 20° C./min in theunconstrained state shifts 6.8° C. to the high temperature side from themelting point of the yarn before drawing, and the melting point thusmeasured is 7° C. higher than that of Comparative Example 3. Further,the degree of crystallinity is higher in Example 3 than in ComparativeExample 3.

Example 4, Comparative Example 4

A quantitative test was performed on eight yarns using a two-stagedrawing device that included two drawing baths in Example 1 as a drawingdevice. For comparison, drawing was performed using two hot aircirculation drawing baths in the same manner. As the drawing properties,the drawing state in an 8-hour operation was evaluated, while thedrawing properties were evaluated for 5 minutes in Examples 1 to 3 andComparative Examples 1 to 3. Table 7 shows the results. The drawingspeed of all the sample yarns except the sample yarn with a draw ratioof 5.6 times in this example was set to 9 m/min (the drawing speed ofthe sample yarn with a draw ratio of 5.6 was 4.8 m/min). In thecomparative example, since the drawing stability was low, the draw ratiohad to be reduced even with two-stage processing. Therefore, in order tomaintain the drawing stability for 8 hours at the above drawing speed,the upper limit of the draw ratio was only 2 times. However, in thedrawing method of this example, the drawing was performed at a drawratio of 2.5 times and was not a problem. When the drawing speed wasreduced, the drawing could be performed even at a draw ratio of 5.6times without any yarn breakage. Moreover, a variation (coefficient ofvariation) in strength of the sample yarns of this example was improved.The sample yarns were drawn at various draw ratios and then taken forDSC measurement. Table 8 shows the results of the measurements. The DSCcharts are shown in FIGS. 5 to 10.

TABLE 7 Example/ Draw Coefficient of Comparative Exper. ratio Drawingstate Strength variation in Elongation Example No. Sample (times) (8hours) (CN/dtex) strength (%) (%) Ex. 4 4-1 110T single-twisted yarn 2.5A: No yarn breakage 37.1 1.51 3.2 4-2 110T single-twisted yarn 5.6 A: Noyarn breakage 38.2 1.36 2.6 Comp. Ex. 4 4-3 110T single-twisted yarn 2.0A: No yarn breakage 35.1 2.76 3.4 4-4 110T single-twisted yarn 2.5 B:The yarn was broken 32.6 5.53 3.2 two times.

TABLE 8 Example/ Draw DSC peak temperature DSC peak temperature Degreeof Comparative Exper. ratio on low temperature on high temperaturecrystallinity DSC chart Example No. Sample (tims) side (° C.) side (°C.) (%) No. Before drawing 4-0 110T single-twisted yarn — ◯ 150.3 — 75FIG. 4A Ex. 4 4-5 110T single-twisted yarn 2.0   151.1 ◯ 158.8 76 FIG. 54-1 110T single-twisted yarn 2.5   151.3 ◯ 158.8 77 FIG. 6 4-6 110Tsingle-twisted yarn 3.0   152.0 ◯ 158.6 79 FIG. 7 4-2 110Tsingle-twisted yarn 5.6 — ◯ 159.1 81 FIG. 8 Comp. Ex. 4 4-7 110Tsingle-twisted yarn 1.5 ◯ 150.5   157.3 78 FIG. 9 4-3 110Tsingle-twisted yarn 2.0 ◯ 151.5   158.6 78 FIG. 10 (Note) ◯ Maximum peaktemperature (melting point)

As is evident from Tables 7 to 8 and FIGS. 5 to 10, in the drawingmethod of this example, the main peak appears on the high temperatureside even at a low draw ratio of about 1.5 times. On the other hand, inthe conventional drawing method (Comparative Example 4 and FIGS. 9 to10), although a small peak is observed on the high temperature side at adraw ratio of 2 times, the main peak temperature is substantiallyunchanged from the peak temperature before drawing. Thus, the resultsconfirmed that there is a difference between the yarns of this exampleand the yarns by the conventional drawing method in terms of a change inthe fine structure of the yarn.

As described above, the drawing method of the present invention isclearly distinguished from the hot air circulation drawing method inthat the maximum draw ratio at which a yarn breakage may occur is higherunder the same drawing conditions. This results in the followingpractical advantages.

(1) The present invention can provide a fine high strength polyolefinyarn at a high draw ratio, which has been difficult to produce.

(2) The present invention can suppress a yarn breakage and fuzz even atthe same draw ratio, and therefore can reduce a defective rate, a loss,and a variation in the physical properties.

(3) Since low-cost yarns with a large fineness can be used as feedyarns, the material costs can be reduced.

Industrial Applicability

The drawn yarns obtained by the drawing method of the present inventionare suitable for ropes, fishing lines, reinforcing materials, protectiveclothing, or the like. Moreover, since the drawn yarns cannot be seeneasily by the naked eye and have high tenacity, they are suitable forstrings for hanging, sutures, thin knitted fabrics, nets, or the like.

Description of Reference Numerals

1 Yarn Feeder

2 First Roller Group

3 Drawing Bath

4 Second roller group

5 Winder

6 Heater for circulating liquid

7 Pump

8, 10 a-10 c Feed Yarn

9, 11 a-11 c Drawn Yarn

12 Inner Wall of Drawing Bath

13 Jacket Portion

14 Yarn Path

15 Miner Axis, Height, or Diameter of Yarn Path

16 Housing Portion of Drawing Bath

1. An ultrahigh molecular weight polyolefin yarn that has been drawn,having a melting point that is determined as a maximum peak temperaturemeasured by a differential scanning calorimeter (DSC) at a temperaturerise rate of 20° C./min in an unconstrained state, wherein the meltingpoint is higher than a melting point of the yarn before drawing.
 2. Theultrahigh molecular weight polyolefin yarn according to claim 1, whereinthe melting point of the drawn ultrahigh molecular weight polyolefinyarn is at least 5° C. higher than the melting point of the yarn beforedrawing.
 3. The ultrahigh molecular weight polyolefin yarn according toclaim 1, wherein the drawn ultrahigh molecular weight polyolefin yarnhas a total fineness of 50 dtex or less and a coefficient of variationin strength of 2% or less.
 4. The ultrahigh molecular weight polyolefinyarn according to claim 1, wherein the ultrahigh molecular weightpolyolefin is ultrahigh molecular weight polyethylene.
 5. The ultrahighmolecular weight polyolefin yarn according to claim 4, wherein theultrahigh molecular weight polyethylene yarn has been drawn and has amaximum melting peak temperature of 155 to 162° C., which is measured bya differential scanning calorimeter (DSC) at a temperature rise rate of20° C./min in an unconstrained state.
 6. The ultrahigh molecular weightpolyolefin yarn according to claim 4, wherein the drawn ultrahighmolecular weight polyethylene yarn has a degree of crystallinity of 76to 85%, which is determined from heat of fusion measured by adifferential scanning calorimeter (DSC) at a temperature rise rate of20° C./min in an unconstrained state.
 7. A method for producing anultrahigh molecular weight polyolefin yarn comprising: heating anddrawing the ultrahigh molecular weight polyolefin yarn, wherein adrawing bath that includes a hollow yarn path and a jacket portion inwhich a heated liquid circulates is placed in a drawing zone, positiveair ventilation is not provided in the yarn path, and the yarn is heatedby radiant heat from the jacket portion and natural convection, anambient temperature of the drawing bath is 150 to 157° C. and iscontrolled within ±0.2° C., and the yarn is heated and drawn whilepassing through the yarn path in a non-contact manner.
 8. (canceled) 9.The method for producing an ultrahigh molecular weight polyolefin yarnaccording to claim 7, wherein a draw ratio in the drawing zone is 1.5 to10 times.
 10. (canceled)
 11. The method for producing an ultrahighmolecular weight polyolefin yarn according to claim 7, wherein the yarnbefore drawing is an untwisted yarn, an interlaced yarn, a twisted yarn,or a braided yarn.
 12. The method for producing an ultrahigh molecularweight polyolefin yarn according to claim 7, wherein the yarn beforedrawing has a fineness of 400 dtex or less.
 13. A method for producingan ultrahigh molecular weight polyolefin yarn comprising: drawing a rawyarn before braiding by the drawing process according to claim 7; andsubsequently braiding at least part of the drawn yarn.
 14. A method forproducing an ultrahigh molecular weight polyolefin yarn comprising:drawing a raw yarn before braiding by the drawing process according toclaim 7; subsequently braiding at least part of the drawn yarn; andfurther drawing the braided yarn.
 15. A drawing device used in themethod for producing an ultrahigh molecular weight polyolefin yarnaccording to claim 7, comprising: a feeder for feeding a yarn; a drawingbath for heating and drawing the yarn; a winder for winding up the drawnyarn, wherein the drawing bath includes a hollow yarn path and a jacketportion in which a heated liquid circulates.
 16. The drawing deviceaccording to claim 15, wherein the heated liquid is heated outside thedrawing bath, and is circulated by a pump.
 17. The drawing deviceaccording to claim 15, wherein the yarn path has a height or diameter of5 to 300 mm, and the drawing bath has a length of 0.3 to 10 m.